Astronomers Discover Potentially Earthlike Planet Orbiting Binary Star | Hacker News Reader

Astronomers Discover Potentially Earthlike Planet Orbiting Binary Star

technologyreview.com

93 pointsJohnIdol31 comments

Sensationalist headline. Actually just a candidate for supporting liquid water (and then only for some of it's fairly elliptic orbit).

And it's pretty damn big, so not likely to be a rock, more like a gas giant (If it _doesn't _ have a large gaseous atmosphere it would I think be the biggest rock planet ever discovered.)

So "habitable exo-planet" is stretching things............... a lot.

This has become a common pattern with exo-planet reporting.

Often they are reported to be "earth like" or "habitable" when they only have potential for liquid water.

Also, some of these planets that are reported may not actually exits. See http://en.wikipedia.org/wiki/Gliese_581_g.

Yeah well it's an unfortunate by-product of a) research institutions feeling the pressure to spin their output in a way which is consumer-friendly and b) the publishing industry turning that spin into an absurd attention-grabbing headline.

It's more a by-product of the fact that the Kepler mission has produced so many planet candidates (with an estimated ~50% false positive rate) that it would require about 30 years of telescope time on the world's largest telescopes to actually confirm that the stars have planets.

Can you cite a source for your 50% false positive rate? I found a source[1] that argues for a ten percent false positive rate.

What do you mean to "confirm" that the stars have planets? I could imagine, directly imaging them is confirmation, but, as I understand it, that's nearly impossible for the average exoplanet we've found. What types of data are Kepler and COROT lacking which you desire for confirmation?

[1] http://arxiv.org/abs/1101.5630

The false positive rate seems to have been revised to 40% since I last checked, but my reference is here (though they cite the Morton & Johnson paper, too):

http://adsabs.harvard.edu/abs/2011ApJ...736...19B

The 10% false positive rate is for rank 2 targets, but the majority of targets are rank 4, which have a 40% false positive rate. (See section 2.2.2)

To confirm that the stars have planets, one would do spectroscopic follow up. You would see the slight wobbling of the host star due to the gravitational influence of the planet, and this would manifest itself in a slight Doppler shifting of the spectral lines of the host star. The problem is that most of the stars that Kepler is observing are so faint that ground-based spectroscopic follow-up is impossible except on the largest telescopes, and even then you can only do it for a handful of the thousands of candidates that Kepler is discovering.

By its nature, a big rocky planet could hold on to a thicker atmosphere; it would also have greater internal heat, a thinner crust, so more geologic activity, greater volcanism.

> So "habitable exo-planet" is stretching things............... a lot.

Not to say anything about how hard would it be just to get there.

A red dwarf from 1000 au would only look like a moderately bright star, won't it?

On the other hand, it would be close enough that if aliens inhabited, they could send a probe with present-day human level of technology. That is, the nearby star would serve as a stepping stone and an excuse to bridge the gap to interstellar space. Compare it to our Alpha Centauri, which lies just shy of 300K au, a relatively costly cosmic barrier to entry.

But for our neighbourhood, there is still the possibility of a brown dwarf or Jupiter-sized world lurking in the depths of our Oort cloud. Alternative destinations are 500-750au which would be good spots to place a telescope (exploiting the Sun as a gravitational lens) http://www.centauri-dreams.org/?p=10123 . You need intermediary objectives to make interstellar exploration a more realizable goal.

A red dwarf from 1000 au would only look like a moderately bright star, won't it?

Indeed. The absolute magnitude of 55 Cancri B is 12.66, and the distance between the companions is 1065 AU [1]. Plugging these values to the magnitude equation yields a visual magnitude of about -3.78 [2], a little fainter than Venus at its minimum brightness [3].

[1] http://en.wikipedia.org/wiki/55_Cancri [2] http://orbitsimulator.com/formulas/vmag9.html [3] http://en.wikipedia.org/wiki/Apparent_magnitude#Table_of_not...

I probably did the calculations[1] wrong but the value I'm getting for the apparent magnitude of 55 Cancri B at 1000 AU with an absolute magnitude of 12.66[2] is about -3.9121 which, if located in our Solar system, would be bright enough to see in daylight, despite being almost 35 times as distant as Pluto is to the Sun.

[1] http://ceres.hsc.edu/homepages/classes/astronomy/spring99/Ma... [2] http://en.wikipedia.org/wiki/55_Cancri

Still, it won't look like 'two suns in the sky', but more like Venus.

Definitely. It would look like a pretty damn bright star, but not like a second Sun.

What would the level of light produced by this red dwarf in comparison to, say, the light produced by a full moon on Earth?

Much lower. You can still read off the light of the full moon, barely.

http://en.wikipedia.org/wiki/Apparent_magnitude#Table_of_not...

For comparison's sake, if the Sun were 600au away, it would be as bright as the full moon. This red dwarf is much less luminous as it is, being at 1000au would make it bright, but unremarkable.

To put things more into prespective, this red dwarf at 1000au distance would be as bright as our Sun 50K au away (or 0.8 ly away).

Maybe in 50 years we can get probes up to 10% light speed.

200-250 years to reach the planet and then another 20 years for the signal to get back (if we can somehow make a signal strong enough).

So 300 years from now our great-great-grandchildren might know (that's 70 years longer than US history).

But we'd actually have to spend some of that war and terrorism industry money on NASA and private investment to accomplish that. Not sure the politicians would ever bother.

"We're left, like the starving donkey equidistant between two bails of hay, unable to decide on what to celebrate" <-- the closest of these things is 20 light years :[

The scale of space is shocking. The fastest man made object, Helios 2 (http://goo.gl/xCow), at 250000kph, would take 17000 years to get to the next nearest star, Alpha Centauri.

This post by Charles Stross is worth a read: http://www.antipope.org/charlie/blog-static/2007/06/the_high...

To quote: "interstellar travel for human beings is near-as-dammit a non-starter"

This is one of those stories that makes my internal 12 year-old want to post the following comment and my 42 year-old too in awe to stop it:

"Cool!"

In the habitable zone 74% of its orbit? Although it sounds great, I'm left skeptical: to support life, wouldn't that need to be 100%?

It doesn't need to be 100% if the atmosphere of the planet could keep enough heat for the remaining 26% of the time, which is entirely likely.

This find is awesome, but it's not what the headline describes. The planet is no "ExoEarth". It's a fantasticly cool exoplanet that could very probably support life that vaguely resembles life on Earth (not humans, though).

It looks like the planet actually slides closer in to the star, thus the issue would be keeping the environment cool enough.

Closer to a smaller, cooler star.

Yes, but the habital zone scales with star size, so a radial position less than the habital zone would indeed be warmer than desirable for Earth-like life.

Posted similar comment directly to the article. Quite pleased with myself for noticing a typo without having to check. It's probably "Gliese 581g" without the extra "4" that the author is referring to in the list of top candidates. It proves the point, though, that this is a hot area of astronomy. I'm no expert, but I was familiar enough with the first exasolar discoveries to notice the typo immediately.

"That's weird! The sky on Cancri 55 f must be out of this world. "

Really, that's the quality of writing from MIT Technology Review?

"The sky on Cancri 55 f must be out of this world."

Arrrgh.

The planet was discovered in April 2005, nothing news.

I thought discovery of 55 Cancri f was published in this paper on the 11th of July this year --> http://arxiv.org/abs/1107.1936

Well I guess you're wrong --> http://web.archive.org/web/20061216012023/http://www.aas.org...

It was discovered in April 2005. http://en.wikipedia.org/wiki/55_Cancri_f

Yes, but the 'news' is that it is within the habitable zone. (For certain definitions of habitable.)

Reply on news.ycombinator.com